Torque converters have been known since 1905 (DE 22 14 22 and DE 23 88 04). The inventor, Föttinger, installed a pump and a turbine between two halves of a shell which were joined together in a fluid-tight connection after assembly. In a further refinement of the invention, a stator is also positioned. In the pump, the turbine and the stator there are vanes that extend essentially radially. Filling the housing with a fluid—preferably oil—brings about a transfer of force and torque from the pump to the turbine. The introduction of force into the torque converter in a motor vehicle occurs by having the housing of the converter attached to the crankshaft of a combustion engine in a rotationally fixed connection. The output takes place through the turbine, with the transmission input shaft of the subsequent transmission being connected—directly or indirectly—to the hub of the turbine in a rotationally fixed connection.
Through the rotation of the housing—and hence of the pump—the oil is thrown outward by the effect of centrifugal force. The oil flows in an arc within the pump. In the radially outer area of the pump the oil stream is diverted in the axial direction and then flows into the turbine. The power that the oil must deliver slows the oil flow, so that the flow cross section in the turbine must expand increasingly in the direction of flow. Since the oil must be directed again to the inflow area of the pump, the outer wall of the turbine is curved toward the inflow area of the pump. Before the stream of oil coming from the turbine can again reach the inflow openings of the pump, the oil also flows through the stator. The stream of oil undergoes another change of direction in the stator, so that the flow against the pump vanes is optimized maximally. The oil circulation can then begin again. As long as the circulation is maintained, and as long as the turbine rotates at a lower speed than the pump, torque can be transmitted. However, the closer the turbine speed approaches the pump speed, the poorer the efficiency becomes.
The pump, the turbine and the stator together form the torus of a torque converter. The corresponding flow is then a toroidal flow. The concept is derived from mathematics, since the rotating ring of oil at the same time rotates around the rotational axis of the torque converter with its axis offset.
Since the invention of the torque converter, additional important components have been invented and added to the torque converter. The bridging clutch, for example, represents an important improvement, since it can be actuated when efficiency is low. As a result, the power flows—directly or indirectly—into the transmission shaft. Another known improvement provides for a torsion vibration damper—called a damper for short—to be installed in the power path, so that inconsistencies in the rotation of the crankshaft do not reach the transmission input shaft.
Also, many shapes for the torus have been invented in the last hundred years, in order to improve the efficiency of the torque converter. But in recent years a standard shape has evolved for the motor vehicle, which has now been adapted essentially only to the power requirement and to the possibilities for installation in the transmission.